There are many examples of different types of cellular networks which provide for user equipment to connect to the network. In an UMTS cellular network, the User Equipment (UE), such as a cellular phone or wireless computing device (handheld or installed in static equipment), connects by carrying out an “attach” procedure with a base station of a cell, starting with repeated requests (preambles) on the Random Access Channel until the request is acknowledged. The successful conclusion of this sequence is known as “UE attach” or “MM attach”.
Currently, all devices which connect to cellular wireless networks in order to transfer data are deemed to require bi-directional data transfer and mobility management. When a UE powers on, an ATTACH procedure is initiated towards the selected network so as to enable network and UE to execute its mobility management functionality and manage service requests for data transfer to and from the UE.
To support this procedure a signaling connection must first be established to configure the appropriate radio bearers to support the data transfer. This involves an RRC Connect Establishment Procedure which is executed between the UE and the UTRAN. In order to support the NAS signaling associated with an MM ATTACH procedure, an Initial Direct transfer Procedure is initiated between UE and UTRAN.
The MM Attach Procedure consists of an MM-ATTACH REQUEST message, which is embedded in the INITIAL DIRECT TRANSFER message between UE and UTRAN. When the UTRAN receives the INITIAL DIRECT TRANSFER message, it establishes a signaling connection with the CORE network in order to support transfer of the NAS signaling for the MM-ATTACH REQUEST message. Assuming the UE is authorized to attach to network, an MM-ATTACH ACCEPT message is sent from the CORE network to the UE via the UTRAN, embedded in a DOWNLINK DIRECT TRANSFER message.
As there are predictions of 50 billion connected devices by 2020, and predictions that M2M (machine to machine) enterprise will be a significant part of this, operator networks will require a significant increase in capacity to meet market demands. Spectrum availability is limited and so this may limit capacity of the networks. Required capacity from an operator's perspective is influenced by the volume of devices requiring connectivity. Today operators assume that all mobiles require an ‘always on’ connectivity model. In other words, if an operator has 5 million subscribers in his network, it must be dimensioned to support connectivity for all 5 million subscribers concurrently. Currently this assumption is also made for M2M connectivity. Having UEs connected to the network takes up resources such as processing and data storage resources for maintaining a record of the identities and locations of the connected UEs in the network, and takes up some bandwidth for periodic wireless communications with the UE to check it is still there and to check its signal strength for example.